Change first() and second() in CSSPairValue to return const references

Source/core/animation/LengthPairStyleInterpolationTest.cpp

Index: Source/core/animation/LengthPairStyleInterpolationTest.cpp
diff --git a/Source/core/animation/LengthPairStyleInterpolationTest.cpp b/Source/core/animation/LengthPairStyleInterpolationTest.cpp
index 6d3b8f140d531f3be0f4b086163a9fc431423d50..72de950ed0dedb747ad065c1d188865f18a3232b 100644
--- a/Source/core/animation/LengthPairStyleInterpolationTest.cpp
+++ b/Source/core/animation/LengthPairStyleInterpolationTest.cpp
@@ -35,15 +35,13 @@ protected:
     static void testPrimitiveValue(RefPtrWillBeRawPtr<CSSValue> value, double first, double second, CSSPrimitiveValue::UnitType unitType)
     {
         EXPECT_TRUE(value->isValuePair());
+        const CSSValuePair& pair = toCSSValuePair(*value);
 
-        CSSValuePair* pair = toCSSValuePair(value.get());
-        ASSERT_TRUE(pair);
+        EXPECT_EQ(toCSSPrimitiveValue(pair.first()).getDoubleValue(), first);
+        EXPECT_EQ(toCSSPrimitiveValue(pair.second()).getDoubleValue(), second);
 
-        EXPECT_EQ(toCSSPrimitiveValue(pair->first())->getDoubleValue(), first);
-        EXPECT_EQ(toCSSPrimitiveValue(pair->second())->getDoubleValue(), second);
-
-        EXPECT_EQ(toCSSPrimitiveValue(pair->first())->typeWithCalcResolved(), unitType);
-        EXPECT_EQ(toCSSPrimitiveValue(pair->second())->typeWithCalcResolved(), unitType);
+        EXPECT_EQ(toCSSPrimitiveValue(pair.first()).typeWithCalcResolved(), unitType);
+        EXPECT_EQ(toCSSPrimitiveValue(pair.second()).typeWithCalcResolved(), unitType);
     }
 };